1. Field of the Invention
The present invention relates to a soundproof body suitable for soundproofing noise, and to an insulator for a motor vehicle suitable for soundproofing noise which propagates into a compartment of the motor vehicle, noise occurring in the compartment of the motor vehicle, or the like.
2. Description of the Related Art
Conventionally, in a soundproof body of this type, a soundproof material described in JP H07-081007A has been proposed. This soundproof material is constructed by laminating a skin layer, a first felt layer, an intermediate sheet layer, and a second felt layer in sequence.
Here, the skin layer is formed from, for example, a polyvinyl chloride resin sheet. The first felt layer is made of polypropylene resin felt. The intermediate sheet layer is formed from a polyvinyl chloride resin sheet, similarly to the skin layer.
In the intermediate sheet layer, vent openings are formed at an opening ratio in a predetermined range so as to attenuate vibration propagating from the second felt layer to the first felt layer. The second felt layer is made of reproduction cotton felt.
The soundproof material constructed in such a manner is arranged as a dash insulator along a dash panel which isolates an engine room and a compartment of a motor vehicle or a vehicle compartment from each other.
Herein, the dash insulator is fixed at its second felt layer to the dash panel and is located at the second felt layer, the intermediate sheet layer, the first felt layer, and the skin layer in this order in the vehicle compartment in order to soundproof the interior of the vehicle compartment from noise occurring in the engine room.
Incidentally, in the dash insulator constructed in the above manner, the first and second felt layers are made of felt as previously described. Thus, the first and second felt layers have air-permeability. Furthermore, the intermediate sheet layer has air-permeability because it has vent openings.
In this way, in the dash insulator, the first and second felt layers and the intermediate sheet layer are air-permeability. When noise, therefore, pass through the dash insulator, for instance, the intermediate sheet layer and the first felt layer of their laminating construction induce a resonance phenomenon which they promote vibrations together with each other under noise of low frequency range.
As a result, noise passing through the dash insulator from the second felt layer to the skin layer is increased, thereby to reduce transmission sound loss of noise in the dash insulator is reduced. This causes drawbacks that induce deterioration of soundproof effects as the dash insulator.